获得客户端真实的IP地址

function GetIP(){
    if (getenv("HTTP_CLIENT_IP") && strcasecmp(getenv("HTTP_CLIENT_IP"), "unknown"))
        $ip = getenv("HTTP_CLIENT_IP");
    else if (getenv("HTTP_X_FORWARDED_FOR") && strcasecmp(getenv("HTTP_X_FORWARDED_FOR"), "unknown"))
            $ip = getenv("HTTP_X_FORWARDED_FOR");
         else if (getenv("REMOTE_ADDR") && strcasecmp(getenv("REMOTE_ADDR"), "unknown"))
                  $ip = getenv("REMOTE_ADDR");
              else if (isset($_SERVER['REMOTE_ADDR']) && $_SERVER['REMOTE_ADDR'] && strcasecmp($_SERVER['REMOTE_ADDR'], "unknown"))
                       $ip = $_SERVER['REMOTE_ADDR'];
                   else
                       $ip = "unknown";
    return($ip);
}


即使用户通过代理服务器上网，也能查出他的IP。但是要求代理服务器的类型是transparent类型。如果代理服务器是anonymous或者是high anonymous类型，HTTP_X_FORWARDED_FOR也无能为力了。